A D.C. woman who drowned her 6-year-old son several years ago in a high-profile case walked away from St. Elizabeths Hospital on Saturday after a security guard failed to ask her for identification, a hospital official said Sunday.

Julia Barber, 36, who in 2007 was found not guilty by reason of insanity to the 2005 killing of her son, Donmiguel Nathaniel Wilson Jr., left the grounds of the D.C. psychiatric hospital, where she had been committed, and returned on her own around 9 p.m Sunday.

Barber is the third patient to walk off the hospital grounds without authorization since February.

Barber left the hospital grounds at 10:47 a.m. Saturday, according to Phyllis Jones, a spokeswoman with the D.C. Department of Behavioral Health. Jones said Barber had an hour of “ground privileges,” during which she was allowed to walk around the campus with a security escort. Jones said Barber walked out the hospital’s exit on Alabama Avenue SE. The hospital had notified Barber’s family as well as D.C. police, Jones said.

St. Elizabeths has been under scrutiny recently for a string of security lapses involving patients leaving the hospital without authorization. In February, Eric Izlar, 42, who was charged with aggravated assault in 1998, “jogged” off the hospital’s campus and was missing for about a week before he returned. Also in February, Daniel Ellis, 56, a patient who had voluntarily committed himself to the hospital, was found dead under a pile of snow after he walked off the property. Ellis left the hospital without obtaining a proper discharge, officials said.

The hospital reportedly changed its security procedures in February after the second patient fled. Hospital officials said it began requiring security officers to check the identification of all individuals leaving the hospital. Jones said one of the security officers failed to check Barber’s identification. That officer, Jones said, was fired Saturday evening.

In February, D.C. Council member Tommy Wells (D-Ward 6) said he was troubled by the hospital’s lack of security and feared for not only the patients who slipped away from hospital and missed medication and treatment, but also for the community.

On Monday, hospital officials are expected to testify before the council during a hearing on the hospital’s 2015 fiscal budget. Hospital officials expect the recent string of patients leaving without authorization to be discussed.

Jones said Sunday that most patients who leave the hospital eventually return on their own, as opposed to having U.S. marshals apprehend them.

Last year, Barber petitioned the court to be allowed to leave the hospital for approved visits with her family. In court filings through her attorney, Barber said her condition had improved and that she wanted to spend time away from the hospital with family members. During a series of court hearings, prosecutors repeatedly objected to Barber’s request, saying she was still a danger. In March, D.C. Superior Court Judge Erik P. Christian denied the request and ordered Barber to remain hospitalized.

According to court documents, Barber was plagued by mental problems and drug addiction and began deteriorating precipitously in the weeks before she killed her son, denying herself food and sleep, talking to herself and telling others that she was hearing voices.

About 8:30 a.m. on July 18, 2005, in an apartment in the 3200 block of Wheeler Road SE, Donmiguel’s grandmother found the boy in a bathtub full of water, the home otherwise empty. His wrists and ankles were bound with duct tape. His hands were tied behind his back with a bandana. His ankles were tied with lingerie. And from the residue on his face and the used duct tape in the tub, it appeared that he had been gagged.

On the morning his body was discovered, Barber could not be found. She surfaced later that day and quickly became the suspect in her son’s death. Initially, she tried to cast suspicion on an ex-boyfriend, but she eventually admitted that she had killed Donmiguel, “who had been bad all day,” according to an affidavit in the case.

Barber was taken for an emergency evaluation after her behavior became erratic, and psychiatrists subsequently found her to be mentally ill and a danger to herself and others. She was then taken to St. Elizabeths.